Regulation of nitrate reductase in the basidiomycete Ustilago maydis

Nitrate reductase was induced in Ustilago maydis by growth in medium containing only nitrate as the nitrogen source. Ammonium ions repressed the enzyme and led to a rapid loss of activity. Ammonium did not inhibit the enzyme in vitro; although amino acids partially did so, this cannot account for the rapid loss of in vivo activity which occurred when the ammonium was added. Experiments with cycloheximide and actinomycin D, together with measurements of protein turnover, suggested that nitrate reductase is actively broken down when cells with fully induced activity are transferred to medium containing ammonium ions.

Coronary arteriographic appearances in patients with left bundle-branch block

Left bundle-branch block (LBBB) was found to be associated with an unusually short left main coronary artery in 11 of 12 patients studied by selective coronary arteriography. The average length of the left coronary artery in this group of 12 patients with LBBB was 4.5 ± 1.7 mm as compared to 12.8 ± 0.8 mm in a control group. Four of the 12 had evidence of ischemic heart disease, one had mild aortic regurgitation, one had myocardiopathy, and one had a patent ductus arteriosus. No etiology was discovered for the LBBB in the remaining five patients. Mechanical and hemodynamic explanations for this association of a particular pattern of coronary anatomy with LBBB are proposed.